1. Technological Field
The present invention relates to a wheel slip control system for a vehicle in which the power of an internal combustion engine is controlled in order to control the rotational speed of driven wheels as well as to control the hydraulic braking system for driven wheels during acceleration slip.
2. Prior Art
Various kinds of wheel slip control devices for vehicles which control the slip of wheels during acceleration
have been proposed and developed. In such a device, it is considered that the power control of the internal combustion engine is adjusted via a sub-throttle valve or a linkless throttle valve provided other than a main throttle valve, connected to an accelerator upon generation of acceleration slip regardless of an operation of the accelerator. Direct control is applied to use the hydraulic braking system installed in the vehicle. Other means, for example, indirect control is adapted to use the delay of ignition timing, thus the driven wheel speed is controlled within an optimal range , thereby preventing the acceleration slip.
However, the wheel slip control systems mentioned above are still inert, and the following problems remain unsolved. The prior wheel slip control system having the subthrottle valve or the linkless throttle valve cannot reduce the torque immediately, due to residual air in an intake pipe, even if the systems begin to close the throttle valve upon sensing acceleration slip, thus the above-mentioned time delay results in over-control.
The prior braking systems for preventing acceleration slip are not sufficient for controlling the wheel speed and require a specific apparatus. If the gear position is in first gear and the driving force is great, extremely high pressure is required to provide a braking force against the driving force. Furthermore, high durability is required for brake pads, and the special brake system having high brake power is required, since the braking system generates high heat due to the great consumption of energy.
In the ignition control to prevent the slip, the delay of rising and dropping in engine torque is less than that of the above-mentioned sub-throttle valve system. The special braking system is not required, however, such a control is not as effective on the surface of a low frictional coefficient such as muddy, icy and snowy roads because of the narrow control range of the engine torque.